Dili: A veteran guerrilla commander is heading for a decisive victory in East Timor's presidential elections and is expected to be sworn in as the country's next head of state in May.

Francisco "Lu-Olo" Guterres had received 57 per cent of the national vote with 90 per cent of votes counted in Monday's election.

Mr Guterres's campaign was backed by Fretilin, the party that led East Timor's revolutionary struggle to independence, and the country's behind-the-scenes powerbroker Xanana Gusmao.

His election is a vote of confidence in a government of national unity that was formed by Mr Gusmao in 2015 comprising Fretilin and the National Congress for Timorese Reconstruction (CNRT).

Michael Leach, an expert on East Timor from Victoria's Swinburne University, said the strong support for Mr Guterres shows the "power-sharing combination of CNRT and Fretilin remains strongly competitive".

Despite that voting was not compulsory, hundreds of thousands of Timorese waited patiently in long queues in blistering heat to vote for a new president for a five-year term ahead of general elections in July.

The elections will be a key to the future of Asia's newest democracy amid concerns the half-island nation's oil and gas revenues are rapidly running dry.

Running second in the unofficial count with 32 per cent of the vote on Tuesday was Democratic Party politician Antonio da Conceicao, the 53-year-old current education minister who says he represents a younger generation of Timorese demanding a change of leadership in the country where poverty remains endemic and there are growing concerns about corruption.

He also campaigned to the build the nation "from the grass roots" by ensuring the majority of people who live in rural areas have enough food, access to markets, schools, clinics, and water and sanitation.

Mr Guterres, 62, who had contested the presidency in three previous elections, needed to get more than 50 per cent of the vote to avoid a run-off election in April.

He received only 30 per cent of first round votes in 2007 and 2012 elections.

The president is largely a ceremonial post but the incumbent Jose Maria de Vasconcelos, also known as Taur Matan Ruak, has spoken out about corruption and insisted on revision of the government's budget.

Mr Vasconcelos is expected to contest the July vote as head of the newly formed People's Liberation Party (PLP).

"President Ruak and his PLP have the best part of four months to make inroads," Professor Leach said.

East Timor has 744,613 registered voters in a population of 1.26 million.